The invention relates to a method for selectively metallizing surfaces of dielectric, non-conductive substrates, and more particularly for electrolessly plating the substrates with copper.
A process of selectively metallizing substrates is disclosed in U.S. Pat. No. Re. 28,042 to Rhodenizer et al.
U.S. Pat. Nos. Re. 28,042, 3,293,109 to Luce et al, 3,522,085 to Watanabe and 4,358,479 to Canestaro et al relate to methods of pre-conditioning a non-conductive surface of a plastic substrate by laminating a metal foil to the surface.
The etching of copper foils (e.g., with an acidic solution of CuCl.sub.2) is disclosed in U.S. Pat. Nos. 2,908,557 to Black et al, 3,083,129 to Jones et al and 4,358,479.
In U.S. Pat. Nos. 3,563,784 to Innes et al, 3,573,937 to Drotar et al and 4,301,190 to Feldstein, methods of conditioning a non-conductive surface prior to activating are described.
In particular U.S. Pat. No. 3,421,922 to Wilson describes the application of a cationic film forming resin and in the method disclosed in co-pending application, Ser. No. 398,140 filed 7/14/82 to Bupp et al assigned to the assignee of the present application, an acidic solution containing multifunctional positively charged molecules consisting of copolymers of polyacrylamide forming the inert backbone and functionally active tetraalkylammonium compounds are applied prior to the activation.
The following U.S. patents relate to methods of cathodically activating a surface with solutions containing Pd and Sn salts: U.S. Pat. Nos. Re. 28,042; 4,008,343 to Cohen et al; 3,011,920 to Shipley, Jr.; and 3,562,038 to Shipley, Jr. et al. In the last two above-mentioned patents the steps of washing the activated surface with distilled water, then HCl and then again with distilled water are disclosed.
Copper plating baths for electrolessly metallizing activated non-conductive surfaces are described in U.S. Pat. Nos. 3,269,861 to Schneble, Jr. et al, 3,900,599 to Feldstein and 4,152,467 to Alpaugh et al.
The teaching of the prior art as cited above provides effective methods for electrolessly plating copper to non-conductive surfaces of dielectric materials, such as thermosetting to thermoplastic resins and glass. However, the indicated methods require a very high number of process steps. In addition, with the continuing trend to miniaturization, to denser packaging of components and to more complex circuits, it becomes more and more difficult to adhere to the process specifications in using the prior art methods. For these reasons the yield of good products and their reliability decrease. Also the known methods provide no effective way to save components in which defects are detected after electroless plating and into which a considerable amount of money and effort have been invested.
It is therefore an object of the invention to improve the known methods for selective electroless plating of copper to non-conductive surfaces.
It is another object of the invention to provide a simple method for selective electroless plating of copper to non-conductive surfaces.
It is a further object of the invention to provide a method for electrolessly plating reproducibly within small tolerances.
It is still another object of the invention to produce parts reliable in field use and requiring little maintenance.
It is still a further object of the invention to produce high quality copper-plated epoxy panels.
It is also an object of the invention to provide a method for reworking defective parts having already undergone the electroless plating process.